Telecommunications apparatus and methods

ABSTRACT

A method of operating a first terminal device to transmit data to a second terminal device by performing device-to-device communication includes selecting radio resources, on which to transmit the data based on a priority status associated with the data, whereby certain radio resource are reserved for use in association with data classified as high priority. A method of operating the second terminal device to receive data from the first terminal device includes: receiving data from the first terminal device using the selected radio resources; determining if another terminal device is transmitting data on a radio resource which is not selected for transmitting data by the first terminal device and which is reserved for transmitting data classified as having a high priority; and, if so, stopping reception of data from the first terminal device on the selected radio resources and instead seeking to receive further transmissions from the other terminal device.

BACKGROUND

Field

The present disclosure relates to telecommunications apparatus andmethods, and in particular to telecommunications apparatus and methodsfor use in wireless telecommunications systems in which terminal devicesare configured to perform device-to-device communications.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Mobile telecommunication systems, such as those based on the 3GPPdefined UMTS and Long Term Evolution (LTE) architecture, are able tosupport more sophisticated services than simple voice and messagingservices offered by previous generations of mobile telecommunicationsystems. For example, with the improved radio interface and enhanceddata rates provided by LTE systems, a user is able to enjoy high datarate applications such as video streaming and video conferencing onmobile communications devices that would previously only have beenavailable via a fixed line data connection.

The demand to deploy fourth generation networks is therefore strong andthe coverage area of these networks, i.e. geographic locations whereaccess to the networks is possible, is expected to increase rapidly.However, although the coverage and capacity of fourth generationnetworks is expected to significantly exceed those of previousgenerations of communications networks, there are still limitations onnetwork capacity and the geographical areas that can be served by suchnetworks. These limitations may, for example, be particularly relevantin situations in which networks are experiencing high load and high-datarate communications between communications devices, or whencommunications between communications devices are required but thecommunications devices may not be within the coverage area of a network.In order to address these limitations there have been proposedapproaches in which terminal devices (communications devices) within awireless telecommunications system may be configured to communicatedirectly with one another without communications passing through aninfrastructure equipment element, such as a base station. Suchcommunications are commonly referred to as a device-to-device (D2D)communications. It is expected that D2D communications will beintroduced in LTE release-12.

Thus, D2D communications allow communications devices that are insufficiently close proximity to directly communicate with each other,both when within and when outside a network's geographical coverage areaand when a network might have failed. This D2D communications abilitycan allow user data to be more efficiently communicated betweencommunications devices by obviating the need for user data to be relayedby a network entity such as a base station, and also allowscommunications devices that are in sufficiently close proximity tocommunicate with one another when one or both devices may not be withinthe coverage area of a network. The ability for communications devicesto operate both inside and outside of coverage areas makes LTE systemsthat incorporate D2D capabilities well suited to applications such aspublic safety communications, for example. Public safety communicationsmay benefit from a high degree of robustness whereby devices cancontinue to communicate with one another in congested networks and whenoutside a coverage area.

Fourth generation networks have therefore been proposed as a costeffective solution to public safety communications compared to dedicatedsystems such as TETRA (terrestrial trunked radio) which are currentlyused throughout the world.

One issue for consideration for D2D communications is how individualdevices establish which of the available radio resources (e.g. in termsof times and frequencies of transmissions) are to be used for theircommunications. In a conventional LTE network a scheduling entity of abase station controls resource allocations in both downlink and uplink.Communications devices receive signalling from the base station toindicated which radio resources are allocated for their use. Because inthis conventional situation the resource allocations are controlledcentrally, the communications associated with different communicationsdevices can be appropriately coordinated. However, in a D2D scenariothere may be no centralised control of which devices are using whichradio resources (transmission resources), thereby leading to anincreased likelihood of collision and interference, for example due tomore than one terminal device selecting the same radio resources forsimultaneous transmission. Furthermore, it can be difficult toappropriately prioritise transmissions from different terminal devicesoperating in a D2D scenario.

Because of these issues there is a need for improved schemes formanaging D2D communications, for example in the absence of a centralcoordinating entity.

US 2013/0012221 [1] provides an overview of some aspects of D2Dcommunications in an LTE wireless telecommunications network anddiscloses a method in which D2D nodes communicate with each other usingthe same uplink (UL) radio resource that is being used by some othercellular user equipment(s) (UEs). In other words, the UL cellularresources occupied by cellular UEs are reused by D2D nodes in theirshort-range communications. Centralized control of D2D communicationscan be performed by appropriate signalling between a D2D-capable UE andan evolved Node B (eNB), and furthermore devices may inform the eNB ofan importance level for their data which the eNB may take into accountwhen controlling access to radio resources.

US 2012/0265818 [2] discloses a scheme which involves performing beaconbroadcasting in a device-to-device communication network. The approachincludes selecting, by a node capable of entering a device-to-devicecommunication network, a channel for broadcasting wherein the selectionis based on the characteristics of the node and the state of the node.

SUMMARY

According to one aspect of the present disclosure, there is provided amethod of operating a first terminal device to transmit data to a secondterminal device by performing device-to-device communication, whereinthe method comprises: selecting radio resources on which to transmit thedata to the second terminal device based on a priority status associatedwith the data; and transmitting the data to the second terminal deviceusing the selected radio resources.

According to another aspect of the present disclosure, there is provideda terminal device configured to transmit data to a second terminaldevice by performing device-to-device communication, wherein theterminal device comprises a controller unit and a transceiver unitconfigured to operate together to select radio resources on which totransmit the data to the second terminal device based on a prioritystatus associated with the data; and to transmit the data to the secondterminal device using the selected radio resources.

According to another aspect of the present disclosure, there is providedcircuitry for a terminal device configured to transmit data to a secondterminal device by performing device-to-device communication, whereinthe circuitry comprises a controller element and a transceiver elementconfigured to operate together to cause the terminal device to selectradio resources on which to transmit the data to the second terminaldevice based on a priority status associated with the data; and totransmit the data to the second terminal device using the selected radioresources.

According to another aspect of the present disclosure, there is provideda method of operating a second terminal device to receive data from afirst terminal device by performing device-to-device communication,wherein the method comprises: receiving data from the first terminaldevice using radio resources selected by the first terminal device fortransmitting the data; determining if another terminal device istransmitting data on a radio resource which is not selected fortransmitting data by the first terminal device and which is reserved fortransmitting data classified as having a high priority; and, if so,stopping reception of data from the first terminal device on theselected radio resources and instead seeking to receive furthertransmissions from the other terminal device.

According to another aspect of the present disclosure, there is provideda terminal device configured to receive data from a transmittingterminal device by performing device-to-device communication, whereinthe terminal device comprises a controller unit and a transceiver unitconfigured to operate together to: receive data from the transmittingterminal device using radio resources selected by the first terminaldevice for transmitting the data; determine if another terminal deviceis transmitting data on a radio resource which is not selected fortransmitting data by the transmitting terminal device and which isreserved for transmitting data classified as having a high priority;and, if so, to stop reception of data from the transmitting terminaldevice on the selected radio resources and instead seek to receivefurther transmissions from the other terminal device.

According to another aspect of the present disclosure, there is providedcircuitry for a terminal device configured to receive data from atransmitting terminal device by performing device-to-devicecommunication, wherein the circuitry comprises a controller element anda transceiver element configured to operate together to cause theterminal device to: receive data from the transmitting terminal deviceusing radio resources selected by the first terminal device fortransmitting the data; determine if another terminal device istransmitting data on a radio resource which is not selected fortransmitting data by the transmitting terminal device and which isreserved for transmitting data classified as having a high priority;and, if so, to stop reception of data from the transmitting terminaldevice on the selected radio resources and instead seek to receivefurther transmissions from the other terminal device.

Further respective aspects and features are defined by the appendedclaims.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein likereference numerals designate identical or corresponding parts throughoutthe several views, and wherein:

FIG. 1 provides a schematic diagram illustrating an example of a mobiletelecommunication system;

FIG. 2 provides a schematic diagram illustrating a LTE downlink radioframe;

FIG. 3 provides a schematic diagram illustrating an example of a LTEdownlink radio subframe;

FIG. 4 provides a schematic diagram illustrating an example of a LTEuplink radio subframe;

FIG. 5 schematically represents a wireless telecommunications systemaccording to an embodiment of the disclosure;

FIG. 6A schematically shows a radio frame structure for supportingdevice-to-device communications between terminal devices in accordancewith certain embodiments of the disclosure;

FIG. 6B schematically shows radio resources of the radio frame structureof FIG. 6A selected by a first terminal device for use in makingdevice-to-device transmissions to a second terminal device in accordancewith certain embodiments of the disclosure;

FIG. 7 is a flow diagram schematically representing a mode of operationfor a first terminal device transmitting data to a second terminaldevice in accordance with certain embodiment of the disclosure;

FIG. 8 is a flow diagram schematically representing a mode of operationfor a second terminal device receiving data from a first terminal devicein accordance with certain embodiment of the disclosure; and

FIG. 9 schematically shows a radio frame structure for supportingdevice-to-device communications between terminal devices in accordancewith certain embodiments of the disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a mobile telecommunications network/system 100operating in accordance with LTE principles and which may be adapted toimplement embodiments of the disclosure as described further below.Various elements of FIG. 1 and their respective modes of operation arewell-known and defined in the relevant standards administered by the3GPP (®) body and also described in many books on the subject, forexample, Holma H. and Toskala A [3]. It will be appreciated thatoperational aspects of the telecommunications network which are notspecifically described below may be implemented in accordance with anyknown techniques, for example according to the relevant standards.

The network 100 includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from terminal devices104. Data is transmitted from base stations 101 to terminal devices 104within their respective coverage areas 103 via a radio downlink. Data istransmitted from terminal devices 104 to the base stations 101 via aradio uplink. The core network 102 routes data to and from the terminaldevices 104 via the respective base stations 101 and provides functionssuch as authentication, mobility management, charging and so on.Terminal devices may also be referred to as mobile stations, userequipment (UE), user terminal, mobile radio, and so forth. Base stationsmay also be referred to as transceiver stations/nodeBs/e-nodeBs, and soforth.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division modulation (OFDM) based interface for theradio downlink (so-called OFDMA) and a single carrier frequency divisionmultiple access scheme (SC-FDMA) on the radio uplink.

FIG. 2 shows a schematic diagram illustrating an OFDM based LTE downlinkradio frame 201. The LTE downlink radio frame is transmitted from a LTEbase station (known as an enhanced Node B) and lasts 10 ms. The downlinkradio frame comprises ten subframes, each subframe lasting 1 ms. Aprimary synchronisation signal (PSS) and a secondary synchronisationsignal (SSS) are transmitted in the first and sixth subframes of the LTEframe. A physical broadcast channel (PBCH) is transmitted in the firstsubframe of the LTE frame.

FIG. 3 is a schematic diagram of a grid which illustrates the structureof an example conventional downlink LTE subframe. The subframe comprisesa predetermined number of symbols which are transmitted over a 1 msperiod. Each symbol comprises a predetermined number of orthogonalsubcarriers distributed across the bandwidth of the downlink radiocarrier.

The example subframe shown in FIG. 3 comprises 14 symbols and 1200subcarriers spread across a 20 MHz bandwidth and in this example is thefirst subframe in a frame (hence it contains PBCH). The smallestallocation of physical resource for transmission in LTE is a resourceblock comprising twelve subcarriers transmitted over one subframe. Forclarity, in FIG. 3, each individual resource element is not shown,instead each individual box in the subframe grid corresponds to twelvesubcarriers transmitted on one symbol.

FIG. 3 shows in hatching resource allocations for four LTE terminals340, 341, 342, 343. For example, the resource allocation 342 for a firstLTE terminal (UE1) extends over five blocks of twelve subcarriers (i.e.60 subcarriers), the resource allocation 343 for a second LTE terminal(UE2) extends over six blocks of twelve subcarriers (i.e. 72subcarriers), and so on.

Control channel data can be transmitted in a control region 300(indicated by dotted-shading in FIG. 3) of the subframe comprising thefirst “n” symbols of the subframe where “n” can vary between one andthree symbols for channel bandwidths of 3 MHz or greater and where “n”can vary between two and four symbols for a channel bandwidth of 1.4MHz. For the sake of providing a concrete example, the followingdescription relates to host carriers with a channel bandwidth of 3 MHzor greater so the maximum value of “n” will be 3 (as in the example ofFIG. 3). The data transmitted in the control region 300 includes datatransmitted on the physical downlink control channel (PDCCH), thephysical control format indicator channel (PCFICH) and the physical HARQindicator channel (PHICH). These channels transmit physical layercontrol information. Control channel data can also or alternatively betransmitted in a second region of the subframe comprising a number ofsubcarriers for a time substantially equivalent to the duration of thesubframe, or substantially equivalent to the duration of the subframeremaining after the “n” symbols. The data transmitted in this secondregion is transmitted on the enhanced physical downlink control channel(EPDCCH). This channel transmits physical layer control informationwhich may be in addition to that transmitted on other physical layercontrol channels.

PDCCH and EPDCCH contain control data indicating which subcarriers ofthe subframe have been allocated by a base station to specific terminals(or all terminals or subset of terminals). This may be referred to asphysical-layer control signalling/data. Thus, the PDCCH and/or EPDCCHdata transmitted in the control region 300 of the subframe shown in FIG.3 would indicate that UE1 has been allocated the block of resourcesidentified by reference numeral 342, that UE2 has been allocated theblock of resources identified by reference numeral 343, and so on.

PCFICH contains control data indicating the size of the control region(i.e. between one and three symbols for channel bandwidths of 3 MHz orgreater and between two and four symbols for channel bandwidths of 1.4MHz).

PHICH contains HARQ (Hybrid Automatic Request) data indicating whetheror not previously transmitted uplink data has been successfully receivedby the network.

Symbols in a central band 310 of the time-frequency resource grid areused for the transmission of information including the primarysynchronisation signal (PSS), the secondary synchronisation signal (SSS)and the physical broadcast channel (PBCH). This central band 310 istypically 72 subcarriers wide (corresponding to a transmission bandwidthof 1.08 MHz). The PSS and SSS are synchronisation signals that oncedetected allow a LTE terminal device to achieve frame synchronisationand determine the physical layer cell identity of the enhanced Node Btransmitting the downlink signal. The PBCH carries information about thecell, comprising a master information block (MIB) that includesparameters that LTE terminals use to properly access the cell. Datatransmitted to terminals on the physical downlink shared channel(PDSCH), which may also be referred to as a downlink data channel, canbe transmitted in other resource elements of the subframe. In generalPDSCH conveys a combination of user-plane data and non-physical layercontrol-plane data (such as Radio Resource Control (RRC) and Non AccessStratum (NAS) signalling). The user-plane data and non-physical layercontrol-plane data conveyed on PDSCH may be referred to as higher layerdata (i.e. data associated with a layer higher than the physical layer).

FIG. 3 also shows a region of PDSCH containing system information andextending over a bandwidth of R344. A conventional LTE subframe willalso include reference signals which are discussed further below but notshown in FIG. 3 in the interests of clarity.

The number of subcarriers in a LTE channel can vary depending on theconfiguration of the transmission network. Typically this variation isfrom 72 sub carriers contained within a 1.4 MHz channel bandwidth to1200 subcarriers contained within a 20 MHz channel bandwidth (asschematically shown in FIG. 3). As is known in the art, data transmittedon the PDCCH, PCFICH and PHICH is typically distributed on thesubcarriers across the entire bandwidth of the subframe to provide forfrequency diversity.

FIG. 4 is a schematic diagram which illustrates some aspects of thestructure of an example conventional uplink LTE subframe. In LTEnetworks the uplink wireless access interface is based upon a singlecarrier frequency division multiple access (SC-FDMA) interface anddownlink and uplink wireless access interfaces may be provided byfrequency division duplexing (FDD) or time division duplexing (TDD),where in TDD implementations subframes switch between uplink anddownlink subframes in accordance with predefined patterns an in FDDimplementations the uplink and downlink channels are separated byfrequency. Regardless of the form of duplexing used, a common uplinkframe structure is utilised. The simplified representation of FIG. 4illustrates such an uplink frame at different levels of resolution witha frame of the uplink frame structure represented at the bottom of thefigure, a subframe represented in the middle of the figure, and a slotrepresented at the top of the figure. Thus the frame 400 is divided into 10 subframes 401 of 1 ms duration where each subframe 401 comprisestwo slots 402 of 0.5 ms duration. Each slot is then formed from sevenOFDM symbols 403 (numbered 0 to 6 in FIG. 4) where a cyclic prefix 404is inserted between each symbol. In FIG. 4 a normal cyclic prefix isused and therefore there are seven OFDM symbols within a subframe,however, if an extended cyclic prefix were to be used, each slot wouldcontain only six OFDM symbols. The resources of the uplink subframes arealso divided into resource blocks and resource elements in a broadlysimilar manner to downlink subframes.

As is well known, each uplink subframe may include a plurality ofdifferent channels, for example a physical uplink shared channel (PUSCH)405, a physical uplink control channel (PUCCH) 406, which may takevarious formats, and a physical random access channel (PRACH). Thephysical Uplink Control Channel (PUCCH) may carry control informationsuch as ACK/NACK to the base station for downlink transmissions,scheduling request indicators (SRI) for terminal devices wishing to bescheduled uplink resources, and feedback of downlink channel stateinformation (CSI) for example. The PUSCH may carry terminal deviceuplink data or some uplink control data. Resources of the PUSCH aregranted via PDCCH, such a grant being typically triggered bycommunicating to the network the amount of data ready to be transmittedin a buffer at the terminal device. The PRACH may be scheduled in any ofthe resources of an uplink frame in accordance with one of a pluralityof PRACH patterns that may be signalled to terminal device in downlinksignalling such as system information blocks. As well as physical uplinkchannels, uplink subframes may also include reference signals. Forexample, demodulation reference signals (DMRS) 407 and soundingreference signals (SRS) 408 may be present in an uplink subframe wherethe DMRS occupy the fourth symbol of a slot in which PUSCH istransmitted and are used for decoding of PUCCH and PUSCH data, and whereSRS are used for uplink channel estimation at the base station. Furtherinformation on the structure and functioning of the physical channels ofLTE systems can be found in reference [3].

In an analogous manner to the resources of the PDSCH for downlinkcommunications, resources of the PUSCH for uplink communications arescheduled or granted by the serving base station. Thus for data is to betransmitted by a terminal device, resources of the PUSCH are granted tothe terminal device by the base station. At a terminal device, PUSCHresource allocation is achieved by the transmission of a schedulingrequest or a buffer status report to its serving base station. Thescheduling request may be made, when there is insufficient uplinkresource for the terminal device to send a buffer status report, via thetransmission of Uplink Control Information (UCI) on the PUCCH when thereis no existing PUSCH allocation for the terminal device, or bytransmission directly on the PUSCH when there is an existing PUSCHallocation for the terminal device. In response to a scheduling request,the base station is configured to allocate a portion of the PUSCHresource to the requesting terminal device sufficient for transferring abuffer status report and then inform the terminal device of the bufferstatus report resource allocation via a DCI in the PDCCH.

Although similar in overall structure to downlink subframes, uplinksubframes have a different control structure to downlink subframes, inparticular an upper region 409 and a lower region 410 ofsubcarriers/frequencies/resource blocks of an uplink subframe arereserved for control signaling (as opposed to the initial symbols for adownlink subframe). Furthermore, although the resource allocationprocedure for the downlink and uplink are similar, the actual structureof the resources that may be allocated may vary due to the differentcharacteristics of the OFDM and SC-FDMA interfaces used in the downlinkand uplink respectively. For example, for OFDM each subcarrier may beindividually modulated and therefore it is not particularly significantwhether frequency/subcarrier allocations are contiguous. However, forSC-FDMA the subcarriers are modulated in combination and therefore itcan be more efficient to allocate contiguous frequency allocations foreach terminal device.

As a result of the above described wireless interface structure andoperation, one or more terminal devices may communicate data to oneanother via a coordinating base station, thus forming a conventionalcellular telecommunications system. Although cellular communicationssystem such as those based on the previously released LTE standards havebeen commercially successful, there are some drawbacks of suchcentralised systems (centralised in the sense of relying on acoordinating base station to route communications from one terminaldevice to another). For example, if two terminal devices which are inclose proximity wish to communicate with each other, uplink and downlinkresources sufficient to convey the data are required. Consequently, twoportions of the system's resources are being used to convey a singleportion of data. A second drawback is that a base station is required tosupport terminal devices that wish to communicate, even when theterminal devices are sufficiently close that one could receive signalsfrom the other with sufficient power to be able to reliably decode thesignals. This drawback can be particularly significant, for example,when a telecommunications system is experiencing high load or basestation coverage is not available, for instance where terminal devicesare out of coverage or when a base station is not functioning correctly.To seek to address some of these issues there has been, as noted above,proposals for supporting device-to-device (D2D) communications.

D2D communications offer the possibility to help address some aspects ofthe aforementioned problems of network capacity and the requirement ofnetwork coverage for communications between LTE devices that can arisein some situations. For example, if user data can be communicateddirectly between terminal devices only one set of resources is requiredto communicate the data rather than both uplink and downlink resources.Furthermore, if terminal devices are capable of communicating directly,terminal devices within range of each other may communicate even whenoutside of a coverage area provided a base station.

FIG. 5 schematically shows a telecommunications system 500 according toan embodiment of the disclosure. The telecommunications system 500 inthis example is based broadly on a LTE-type architecture withmodifications to support device-to-device communications (i.e. directsignalling exchange between terminal devices without data being routedthrough a base station) generally in accordance with previously proposedschemes for D2D communications. As such many aspects of the operation ofthe telecommunications system 500 are already known and understood andnot described here in detail in the interest of brevity. Operationalaspects of the telecommunications system 500 which are not specificallydescribed herein may be implemented in accordance with any knowntechniques, for example according to the established LTE-standards andknown variations and modifications thereof (e.g. to provide support forD2D communications).

The telecommunications system 500 comprises a core network part (evolvedpacket core) 502 coupled to a radio network part. The radio network partcomprises a base station (evolved-nodeB) 504, a first terminal device506 and a second terminal device 508. It will of course be appreciatedthat in practice the radio network part may comprise a plurality of basestations serving a larger number of terminal devices across variouscommunication cells. However, only a single base station and twoterminal devices are shown in FIG. 5 in the interests of simplicity.

As with a conventional mobile radio network, the terminal devices 506,508 are arranged to communicate data to and from the base station(transceiver station) 504. The base station is in turn communicativelyconnected to a serving gateway, S-GW, (not shown) in the core networkpart which is arranged to perform routing and management of mobilecommunications services to the terminal devices in thetelecommunications system 500 via the base station 504. In order tomaintain mobility management and connectivity, the core network part 502also includes a mobility management entity (not shown) which manages theenhanced packet service, EPS, connections with the terminal devices 506,508 operating in the communications system based on subscriberinformation stored in a home subscriber server, HSS. Other networkcomponents in the core network (also not shown for simplicity) include apolicy charging and resource function, PCRF, and a packet data networkgateway, PDN-GW, which provides a connection from the core network part502 to an external packet data network, for example the Internet. Asnoted above, the operation of the various elements of the communicationssystem 500 shown in FIG. 5 may be broadly conventional apart from wheremodified to provide functionality in accordance with embodiments of thedisclosure as discussed herein.

The first and second terminal devices 506, 508 are D2D enabled devicesconfigured to operate in accordance with embodiments of the presentdisclosure as described herein. The terminal devices 506, 508 eachcomprise a transceiver unit 506 a, 508 a for transmission and receptionof wireless signals and a controller unit 506 b, 508 b configured tocontrol the respective terminal devices 506, 508. The respectivecontroller units 506 b, 508 b may each comprise a processor unit whichis suitably configured/programmed to provide the desired functionalityusing conventional programming/configuration techniques for equipment inwireless telecommunications systems. The respective transceiver units506 a, 508 a and controller units 506 b, 508 b are schematically shownin FIG. 5 as separate elements. However, it will be appreciated for eachof the terminal devices the functionality of the terminal devicesreceiver and controller units can be provided in various different ways,for example using a single suitably programmed general purpose computer,or suitably configured application-specific integratedcircuit(s)/circuitry. It will be appreciated the first and secondterminal devices 506, 508 will in general comprise various otherelements associated with their operating functionality in accordancewith established wireless telecommunications techniques (e.g. a powersource, possibly a user interface, and so forth).

The base station 504 comprises a transceiver unit 504 a for transmissionand reception of wireless signals and a controller unit 504 b configuredto control the base station 504. The controller unit 504 b may comprisea processor unit which is suitably configured/programmed to provide thedesired functionality using conventional programming/configurationtechniques for equipment in wireless telecommunications systems. Thetransceiver unit 504 a and the controller unit 504 b are schematicallyshown in FIG. 5 as separate elements for ease of representation.However, it will be appreciated that the functionality of these unitscan be provided in various different ways, for example using a singlesuitably programmed general purpose computer, or suitably configuredapplication-specific integrated circuit(s)/circuitry or using aplurality of discrete circuitry/processing elements for providingdifferent elements of the desired functionality. It will be appreciatedthe base station 504 will in general comprise various other elementsassociated with its operating functionality. For example, the basestation 504 will in general comprise a scheduling entity responsible forscheduling communications. The functionality of the scheduling entitymay, for example, be subsumed by the controller unit 504 b.

Thus, the base station 504 is configured to communicate data with thefirst terminal device 506 over a first radio communication link 510 andcommunicate data with the second terminal device 508 over a second radiocommunication link 512. Both radio links may be supported within asingle radio frame structure associated with the base station 504. It isassumed here the base station 504 is configured to communicate with theterminal devices 506, 508 over the respective radio communication links510, 512 in accordance with the established principles of LTE-basedcommunications. That is to say, in accordance with some exampleimplementations, the device-to-device communications between the firstand second terminal devices may have no impact on the manner in whichthe base station operates in its communications with the terminaldevices.

However, in addition to the terminal devices 506, 508 being arranged tocommunicate data to and from the base station (transceiver station) 504over the respective first and second radio communication links 510, 512,the terminal devices are further arranged to communicate with oneanother (and other terminal devices within the wirelesstelecommunications system) in a device-to-device (D2D) manner over a D2Dradio communication link 514, as schematically indicated in the figure.The underlying principles of the D2D communications supported in thewireless telecommunications system of FIG. 5 may follow any previouslyproposed techniques, but with modifications to support approaches inaccordance with embodiments of the disclosure as described herein.

There are a number of possible approaches to the implementation of D2Dcommunications within an LTE-based wireless telecommunications systemthat have been proposed.

Some approaches may rely on a coordinating entity to allocatetransmission resources for use by respective terminal devices. Forexample, the wireless access interface provided for communicationsbetween terminal devices and base station may be used for D2Dcommunications, where a base station allocates the required resourcesfor D2D communications with control signalling being communicated viathe base station but user data being transmitted directly betweenterminal devices.

Some approaches may not rely on any coordinating entity for managingaccess to radio resources by terminal devices undertaking D2Dcommunications. For example it has been proposed in document R2-133840[4] to use a Carrier Sense Multiple Access, CSMA, to provide a degree ofco-ordination for D2D transmissions by terminal devices throughcontention based scheduling by each terminal device. In effect eachterminal device first listens to identify which resources are currentlybeing used, and then schedules its own transmissions on unusedresources.

Other previously proposed arrangements include those in which a terminaldevice acts as a controlling entity for a group of terminal devices toco-ordinate transmissions of the other members of the group. Examples ofsuch proposals are provided in the following disclosures:

-   -   [5] R2-133990, Network control for Public Safety D2D        Communications; Orange, Huawei, HiSilicon, Telecom Italia    -   [6] R2-134246, The Synchronizing Central Node for Out of        Coverage D2D Communication; General Dynamics Broadband UK    -   [7] R2-134426, Medium Access for D2D communication; LG        Electronics Inc

In another arrangement one of the terminal devices of a group firstsends a scheduling assignment, and then transmits data without a centralscheduling terminal device or controlling entity controlling thetransmissions. The following disclosures provide examples of thisde-centralised arrangement:

-   -   [8] R2-134238, D2D Scheduling Procedure; Ericsson;    -   [9] R2-134248, Possible mechanisms for resource selection in        connectionless D2D voice communication; General Dynamics        Broadband UK;    -   [10] R2-134431, Simulation results for D2D voice services using        connectionless approach General Dynamics Broadband UK

In particular, the last two disclosures listed above, R2-134248 [9],R2-134431 [10], disclose the use of a scheduling channel, used byterminal devices to indicate their intention to schedule data along withthe resources that will be used. The other disclosure, R2-134238 [8],does not use a scheduling channel as such, but deploys at least somepredefined resources to send the scheduling assignments.

Other example arrangements disclosed in [11] and [12] require a basestation to provide feedback to the communications devices to controltheir transmissions. Document [13] discloses an arrangement in which adedicated resource exchanging channel is provided between cellular userequipment and device-to-device user equipment for interference controland resource coordination.

It is to be expected that device-to-device communications will besupported on a radio interface spanning a plurality of frequencies andhaving a radio frame structure comprising a plurality of subframes. Forexample, physical layer signalling associated with device-to-devicecommunications may be implemented using a transmission resource gridhaving similarities to known transmission resource grids, for examplethe uplink and downlink LTE transmission resource grids schematicallyrepresented in FIGS. 3 and 4. For example, it may be expected thatdevice-to-device communications when implemented in the context of anexisting LTE-based wireless telecommunications network will re-usetransmission resources within the LTE uplink frame structure. There arevarious reasons for this. For example, traffic profiles in wirelesstelecommunications systems are typically such an uplink channel is morelikely to have more spare capacity then a downlink channel. Furthermore,the downlink channel is associated with more powerful transmissions froma base station and these are more likely to swamp and interfere withdevice-to-device communications.

Thus, for the example represented in FIG. 5 it is assumed the radiocommunications link 514 that is supporting device-to-devicecommunications between the first terminal device 506 and the secondterminal device 508 is based around a transmission resource gridcomprising a plurality of frequency carriers and a radio frame structurecomprising a plurality of subframes. Physical layer signalling betweenthe first terminal device and the second terminal device may be madeusing transmission resources within this resource grid. However, theexact nature of the transmission resource grid supporting the D2Dcommunications is not significant to the principles underlying theoperation of various embodiments of the disclosure.

One issue which can arise in connection with device-to-devicecommunications, and especially in implementations which do not rely onany central coordinating entity for managing access to radio resources,is a need to allow communications between terminal devices to beprioritised.

For example, in a “walkie-talkie” implementation a first terminal devicemay transmit data to a second terminal device (and possibly otherterminal devices in a broadcast type arrangement) for a relativelyextended period of time (e.g. on the order of seconds or longer) as auser of the first terminal device continues to talk. In implementationswhere there is no central coordination of access to radio resources, thefirst terminal device may in effect select radio resources to use (e.g.in terms of times and frequencies) and announce its intention tocommunicate with the other terminal device(s) using the selected radioresources, and then proceed to do so. The transmitting terminal devicemay continue doing this by continuing to select radio resources andannounce its intention to use these for so long as necessary to transmitthe relevant data. A general example of this approach is described inR2-134238 [8].

The announcement of the selected radio resources (which may be referredto as a scheduling assignment message) can be considered in somerespects to mirror some of the functions of resource allocationsignalling conventionally sent from a base station to terminal devicesin a non D2D scenario. However, one potentially significant differenceis that conventional resource allocations in LTE are generally made by abase station on a per subframe basis. That is to say, resourceallocation signalling in one subframe will typically apply to resourceallocations in one subframe (i.e. the same subframe in downlink or asubsequent subframe in uplink). However, it may be expected for D2Dcommunications that scheduling announcement signalling may apply for anumber of subframes, for example to reduce overall control signallingrequirements.

Scheduling assignment signalling can serve a number of functions. Forexample it can serves to indicate an intended recipient (or recipients)for a data transmission and also inform them of the radio resources theyshould receive and decode to receive the data. A scheduling assignmentmessage can also serve to inform other nearby terminal devices planningto make transmissions about which resources they should preferably avoidto reduce the risk of interference.

The inventors have recognized a drawback of this approach is the firstterminal device can in effect autonomously block the use of certainradio resources for an extended period, and this may be problematic ifthere are other terminal devices needing to make use of the blockedresources to transmit higher priority data. In accordance with currentlyproposed techniques a terminal device wishing to make high prioritytransmissions on resources that have already been claimed for use by afirst terminal device will simply have to wait until the first terminaldevice has completed its transmissions. With this in mind, the inventorshave recognised a need for approaches in a D2D scenario which can allowone terminal device to in effect interrupt transmissions by otherterminal devices, for example because it has urgent (high priority) datato transmit. More generally, the inventors have also recognised a needfor approaches in a D2D communications scenario that allow for theprioritisation of data transmissions by terminal devices, for examplewhereby a terminal device wishing to transmit data associated with arelatively high priority is provided with greater access to theavailable radio resources to transmit the data than a terminal devicewishing to transmit data associated with a relatively low priority.

Thus, in accordance with certain embodiments of the disclosure there isintroduced the concept of radio resources for device-to-devicecommunications which are reserved for use for communicating dataassociated with a certain level of priority. For example, a wirelessinterface for a device-to-device communications link may be supported bya radio frame structure comprising a plurality of subframes, and radioresources corresponding to certain subframes may be reserved forcommunicating data classified as high priority, whereas other subframesmay be used for communicating data not classified as high priority (aswell as data classified as high priority).

FIG. 6A schematically shows a radio frame structure 600 for supportingdevice-to-device communications between the first terminal device 506and the second terminal device 508 across the radio communications link514 schematically represented in FIG. 5 in accordance with an embodimentof the present disclosure. An example mode of operation will bedescribed in which it is assumed the first terminal device 506 wishes totransmit data to the second terminal device 508 in a D2D mode.

The radio frame structure 600 comprises radio resources spanningfrequency and time. The radio resources are divided in time intosubframes, with 12 subframes (labelled SF1 to SF12) represented in thefigure. It will be appreciated this may simply represent an arbitraryseries of subframes in a longer continuous series of subframes. Eachsubframe comprises some radio transmission resources comprising ascheduling allocation region 601 and some radio transmission resourcescomprising a data communication region 602. In this particular examplethe scheduling allocation region 601 is schematically represented asoccurring at the beginning of each subframe and spanning all frequencieswith the data communication region 602 following the schedulingallocation region 601 and again spanning all frequencies. However, itwill be appreciated the exact nature of the radio frame structure andthe manner in which the different regions comprising the radio framestructure, are arranged is not significant to the principles underlyingcertain embodiments of the present disclosure.

The scheduling allocation regions 601 are used by a transmittingterminal device, such as the first terminal device 506 represented inFIG. 5, to indicate transmission resources that are to be used fortransmitting data to another terminal device, such as the secondterminal device 508 represented in FIG. 5. The data communicationregions 602 are used by the transmitting terminal device to transmit theuser-plane data in accordance with the scheduling allocations. In thisrespect, from the point of view of the transmitting terminal device, thescheduling allocation regions 601 may be considered to have somefunctional similarity to PDCCH regions in a conventional LTE downlinksubframe and the data communication regions 602 may be considered tohave some functional similarity to PDSCH regions in a conventional LTEdownlink subframe. However, instead of signalling being exchangedbetween a base station and a receiving terminal device, it is exchangedbetween a transmitting terminal device and a receiving terminal device.The exact manner in which scheduling allocation signalling and datatransmission signalling are configured for a given D2D communicationsimplementation is not significant to the principles underlying certainembodiments of the present disclosure. That is to say, the specificnature of the scheduling allocation signalling, and the manner in whichthe scheduling allocation signalling indicates corresponding resourcesfor data communication, may be in accordance with any appropriatetechnique, such as those previously proposed for device-to-devicecommunications.

A significant aspect of the subframe structure represented in FIG. 6A isthat certain subframes are reserved for high priority communications. Inthis particular example every fourth subframe starting from subframe SF4is assumed to be reserved for high priority data, as schematicallyindicated in FIG. 6A by the shading in the subframes labelled SF4, SF8and SF12. A terminal device wishing to transmit data which is notclassified as high priority is configured to avoid making transmissionsin subframes which are reserved for high priority data. However, aterminal device which has high priority data to transmit may indicatethis by transmitting signalling on radio resources reserved for highpriority communications, i.e. resources in subframes SF4, SF8 and SF12in the example of FIG. 6A. In this regard the time periods reserved forhigh priority communications may be referred to as quiet times. Duringquiet times the terminal devices which do not have high priority data totransmit listen to see if any terminal devices are making transmissions.Transmissions made during quiet times in effect indicate thetransmissions relate to high priority data.

It will be appreciated that what constitutes high priority data may bedifferent for different implementations. In one simple example a user ofa terminal device performing device-to-device communications may simplyindicate the data is high priority, for example by pressing a particularbutton on the terminal device. Thus, in a walkie-talkie implementation auser of the first terminal device may have a routine (non-high priority)conversation with a user of the second terminal device. The firstterminal device will be configured to recognise the data correspondingto the conversation is not high priority and make transmissions at thephysical layer in the subframes which are not reserved for high prioritycommunications. However, a third user of a third terminal device mayhave an urgent message to transmit, and so may press a button on histerminal device to indicate his transmission is urgent (high priority),and begin talking. The third terminal device will be configured torecognise the data corresponding to the urgent message is high priority,and make transmissions in the subframes which are reserved for highpriority communications. Significantly, the presence of the quiet-timesubframes helps to ensure there are available resources for the thirdterminal device to initiate the high priority transmission withoutcolliding with on-going transmissions from other terminal devicesexchanging non-high priority data.

In accordance with some example implementations the classification ofpriority for data may be based on existing 3GPP priority definitions.For example, in accordance with some approaches data priority may bebased on based on QCI (QoS Class Identifier), for example with datatraffic classified as having a low priority relative to controlsignalling traffic. In accordance with some example limitations theapplication of priority for data may be based application based. Forexample, if a user uses an emergency/interruption button of a terminaldevice to indicate a communication should be treated as high priority,an application layer in the terminal device may be configured torecognize this and the traffic correspondingly treated as comprisinghigh priority data. In accordance with some example implementations theclassification of priority for data may be based on what are acceptabledelays for the data. For example, for traffic that is categorized asdelay tolerant (e.g. machine-to-machine application data), the data maybe treated as having relatively low priority. However, for trafficcategorized as real-time (e.g. data associated with a voice/video call),the traffic may be treated as having relatively high priority.

An example operation of device-to-device communications between thefirst terminal device 506 and the second terminal device 508 representedin FIG. 5 using the radio frame structure represented in FIG. 6A willnow be discussed. It will be assumed the first terminal device 506wishes to transmit data to the second terminal device on a generallyongoing basis because the communications correspond with a user of thefirst terminal device speaking to a user of the second terminal devicewith the device-to-device communications being used to support awalkie-talkie type mode of operation. It will further be assumed thatdata in the wireless telecommunications system in which the terminaldevices are operating may be classified as either normal priority orhigh priority. That is to say, the data may be associated with one oftwo priority statuses. Data corresponding to routine communications, forexample a routine conversation, may be considered as having a firstpriority status while urgent data, for example corresponding to a safetyannouncement, or control data needed to ensure continued operation ofthe device-to-device communications (for example because of aconfiguration change for the radio resources used to support D2Dcommunications), may be considered as having a second priority status,where the second priority status indicates a higher priority than thefirst priority status.

FIGS. 6B, 7 and 8 illustrate some aspects of how the device-to-devicecommunications between the first terminal device and the second terminaldevice are implemented in accordance with some example embodiments ofthe disclosure. FIG. 7 is a flow diagram schematically showing somesteps performed by the first (transmitting) terminal device while FIG. 8is a flow diagram schematically showing some steps performed by thesecond (receiving) terminal device. FIG. 6B schematically shows radioresources of the radio frame structure of FIG. 6A selected by the firstterminal device for use in making device-to-device transmissions to thesecond terminal device. It will be appreciated the shading in FIG. 6B isshown across all frequencies in the relevant subframes for ease ofrepresentation, but in practice the first terminal device may not useall frequencies in all the subframes selected for transmission.

Thus, in step S1 represented in FIG. 7, the first terminal deviceidentifies there is data to be transmitted to the second terminal devicein a D2D mode. This may be based, for example, on a user pressing a“transmit” button associated with the first terminal device. However,the exact nature of the data to be transmitted, and the triggering ofthe need to transmit the data, is not significant.

In step S2 represented in FIG. 7, the first terminal device associates apriority status with the data to be transmitted. There are various waysin which the priority status may be determined and some examples arediscussed further below. In this particular example embodiment it isassumed the user of the first terminal device is able to select whetherhis transmission should be classified as having a first priority status(normal priority) or a second priority status (high priority) andindicate this, for example by simply pressing a particular buttonassociated with the terminal device (e.g. an “urgent” button may be usedto indicate a date of high priority). Here it is assumed the user of thefirst terminal device indicates his transmissions are of normalpriority.

In step S3 represented in FIG. 7, the first terminal device selectsradio resources to use for transmitting the data in the manner whichtakes account of the associated priority status. In particular, andreferring to FIG. 6A, the first terminal device avoids using radioresources in the subframes SF4, SF8 and SF12 which are reserved for highpriority data. In this example it is assumed the first terminal devicewishes to use radio resources in all other subframes, as schematicallyindicated by the shading in FIG. 6B. Thus, referring to FIG. 6B, thefirst terminal device transmits data comprising scheduling allocationsignalling in each of the scheduling allocation signalling regions 601of subframes SF1 to SF3, SF5 to SF87, and SF9 to SF11, and makescorresponding user-plane data transmissions in the data communicationregions of these subframes. As noted above, the exact manner in whichthe scheduling allocation signalling indicates the correspondingresources for data communications is not significant. Furthermore, it isnot significant whether the scheduling allocation signalling in aparticular subframe applies to only one subframe or whether it appliesto multiple subframes. An general the specific configuration andoperation in this regard will depend on the particular implementation athand. Furthermore, it will be appreciated the relevant radio resourcesto be used need not all be selected at one time, but these resources maybe selected on an ongoing basis according to ongoing data transmissionrequirements.

In step S4 represented in FIG. 7, the first terminal device transmitsdata to the second terminal device using the selected resources. Thismay be done in accordance with any established device-to-devicecommunications techniques.

In step T1 represented in FIG. 8, the second terminal device beginsreceiving the data that is being transmitted by the first terminaldevice in step S5 of FIG. 7 using the selected radio resources. Againthis may be done in accordance with any established device-to-devicecommunications techniques.

Thus, referring to the example selection of radio resources fortransmission by the first terminal device represented in FIG. 6B, thefirst terminal device begins by transmitting scheduling allocation dataand user-plane data in subframes SF1, SF2 and SF3, and the secondterminal device correspondingly receives these transmissions.

In subframe SF4 (which is reserved for high priority data) the firstterminal device does not make transmissions, and instead seeks to decodeany transmissions from any other terminal devices being made using theseradio resources, as schematically represented by step S5 in FIG. 7.Similarly, in subframe SF4 the second terminal device also listens tosee if there are any other terminal devices making transmissions onthese radio resources, as schematically represented by step T2 in FIG.8.

In effect, subframe SF4 may be considered to represent a quiet timeduring which terminal devices not having urgent data for transmission donot transmit. Thus, a third terminal device which does have urgent datato transmit (or indeed the first or second terminal devices if theyidentify they have urgent data to transmit) may wait until this reservedsubframe to make transmissions. In effect, the provision of the quiettime in subframe SF4 provides an opportunity for terminal devices withurgent data to transmit to interrupt communications from other terminaldevices.

If there are no terminal devices with urgent data to transmit the firstand second terminal devices will not receive any such transmissions insubframe SF4. Thus, in this case the first and second terminal devicesdetermine in their respective steps S5 in FIGS. 7 and T2 in FIG. 8 thatthere is no other terminal device transmitting in the restrictedsubframe SF4, and processing for the first terminal device follows the“no” branch from step S5 to step S6 and processing for the secondterminal device follows the “no” branch from step T2 to step T3. Thedevice-to-device communications between the first and second terminaldevices may then continue in the next subframes that are not reservedfor high priority data, for example subframes SF5, SF6 and SF7, untilthe next “quiet time” is reached in subframe SF8. In subframe SF8 thefirst and second terminal devices in effect behave in the same manner asin subframe SF4. Thus, assuming there are no other terminal devices withurgent data to transmit, the device-to-device communications between thefirst terminal device and second terminal device can continue using theselected radio resources.

However, if there is a terminal device with urgent data to transmit, forexample if there is a third terminal device for which a user hasindicated he has an urgent transmission to make, that terminal devicemay wait until the next quiet time, for example in SF4, SF8 or SF12, tomake transmissions relating to the urgent data (e.g. transmission of thedata itself, or an indication that the first terminal device has urgentdata to transmit and so other terminal devices should not maketransmissions for a period of time following the quiet time. Thetransmissions relating to high priority data during the quiet time (i.e.on the reserved resources) may, for example, have a format correspondingto a conventional scheduling allocation message and be sent in thescheduling allocation region 601 of the relevant subframe, withcorresponding user-plane data, for example comprising the content of theurgent transmission, transmitted in the communication data region 602 ofthe relevant subframe and/or subsequent subframes.

Thus, if in the respective steps S5 in FIG. 7 and T2 in FIG. 8 the firstand second terminal devices receive signalling from a third terminaldevice indicating the third terminal device has urgent (high priority)data to transmit, processing for the first terminal device follows the“yes” branch from step S5 to step S7 and processing for the secondterminal device follows the “yes” branch from step T2 to step T4 inwhich the respective terminal devices respond/react to the interrupt.The exact manner in which the first and second terminal device respondto the interrupt will depend on the implementation at hand.

For example, in some cases the first terminal device may be configuredto cancel any subsequently scheduled data transmissions after receivingan indication that a third terminal device has urgent data to transmit(e.g., cancelling the transmissions scheduled in subframes SF5, SF6 andso on in response to receiving a transmission in subframe SF4). This ineffect frees up the available transmission resources for use by thethird terminal device. The first terminal device may, for example, avoidmaking any further transmissions until it is indicated the urgent datatransmission from the third terminal device is completed. Thisindication may come, for example, in association with informationtransmitted by the third terminal device, for example explicitsignalling to indicate the urgent transmission is complete, or may comefrom the first terminal device determining there are no transmissions ina subsequent subframe reserved for high priority data, for examplesubframe SF8. Once the first terminal device identifies it can re-starttransmissions it may recover from the interrupted state, and proceedwith making transmissions in accordance with whichever recoveryprotocols apply for the application hand.

The urgent transmission from the third terminal device may or may not bedirected to the first terminal device, and the first terminal device maycorrespondingly receive or not receive subsequent transmissions from thethird terminal device associated with the urgent data to be transmitted.

The second terminal device may respond to the interruption by stoppingreception of transmissions from the first terminal device, and insteadseeking to receive further transmissions from the third terminal device.

In some cases the data communication region 602 in a quiet-time subframeused by a terminal device for urgent data may be sufficient tocommunicate the urgent data, in which case the communications betweenthe first and second terminal device might simply continue as normal inthe other subsequent subframes.

Thus approaches in accordance with the principles described aboveintroduce what is in effect an interrupt mechanism for D2Dcommunications whereby a terminal device having data associated with arelatively high priority is provided with an opportunity to transmitthis data by making use of radio resources which are not selected foruse by other terminal devices for transmitting lower priority data. Inbroad summary this is achieved by terminal devices associating apriority status with data to be transmitted in a D2D manner andselecting radio resources on which to transmit the data in a manner thattakes account of the data's priority status, thereby leaving resourcesthat are not selectable for transmitting low priority data available forterminal devices having high priority data to transmit.

A terminal device receiving low priority data from a transmittingterminal device in a device-to-device manner may be configured todetermine if another terminal device is transmitting data on a radioresource which is not selected for transmitting data by the firstterminal device and which is reserved for transmitting data classifiedas having a high priority; and, if so, may stop reception of data fromthe first terminal device on the selected radio resources and insteadseek to receive further transmissions from the other terminal device.

A terminal device having urgent data to transmit may do so by selectingthe resources reserved for high priority data for transmitting eitherthe urgent data itself, or for transmitting an indication that otherterminal devices should restrict their transmissions in some way (e.g.for a particular number of subframes) to allow the terminal devicehaving the urgent data to transmit to do so.

It will be appreciated there may be modifications to the above-describedapproach in accordance with different specific implementations. Forexample, in an implementation in which allocation signalling in onesubframe may relate to radio resources in a data communication region ofanother subframe, the radio resources restricted for high priority datamight only comprise scheduling allocation region radio resources incertain subframes. For example, in a variation of the approach presentedin FIGS. 6A and 6B, the respective data communication regions 601 of thesubframes comprising radio resources which are reserved for highpriority data may be available for use for communicating low prioritydata, but with the scheduling allocation regions in the relevantsubframe remaining reserved. Thus, a scheduling allocation messagetransmitted by the first terminal device in subframe SF1, SF2 or SF3,for example, may be used to allocate resources in the data communicationregion 602 of subframe SF4 for communicating low priority data. However,the scheduling allocation region 601 of subframe SF4 remains reservedfor use in association with high priority data. In such a case, if thefirst terminal device identifies a third terminal device has transmitteda scheduling allocation message using a scheduling allocation regionreserved for use in association with high priority data (e.g. insubframe SF4), the first terminal device may cancel its scheduledtransmission in the data communication region 602 of the relevantsubframe, thereby allowing the terminal device having urgent data totransmit to use these resources. This approach reduces the amount ofradio resources which could otherwise be unused because they arereserved for high priority data when there is no high prioritytransmissions to be made.

The examples described above have focussed on an implementation havingtwo-levels of priority status, that is to say data is either classifiedas non-urgent (and so transmission of the data is avoided on certainresources) or urgent (and so may be transmitted on resources to beavoided for other data). In some other implementations in accordancewith embodiments of the disclosure a greater number of differentpriority levels may be provided to provide for a more general dataprioritisation scheme using similar principles. In effect this may beprovided by applying different restrictions on what radio resources maybe used for transmitting data having different priority status levels.

FIG. 9 schematically shows a radio frame structure 900 supportingprioritisation for device-to-device communications between terminaldevices in accordance with an embodiment of the disclosure.

As with the radio frame structure 600 represented in FIGS. 6A and 6B,the radio frame structure 900 comprises radio resources spanningfrequency and time. The radio resources are divided in time intosubframes, with 12 subframes (labelled SF1 to SF12) represented in thefigure. Each subframe comprises some radio transmission resourcescomprising a scheduling allocation region 901 and some radiotransmission resources comprising a data communication region 902. Inthis particular example the scheduling allocation region 901 isschematically represented as occurring at the beginning of each subframeand spanning all frequencies, while the data communication region 902follows the scheduling allocation region 901, again spanning allfrequencies. However, it will be appreciated the exact nature of theradio frame structure and the manner in which the different regionscomprising the radio frame structure, are arranged is not significant tothe principles underlying certain embodiments of the present disclosure.

The functionality associated with the scheduling allocation regions 901and the data communication regions 902 for supporting D2D communicationsmay be generally in accordance with the principles described above forthe scheduling allocation regions 601 and the data communication regions602 represented in FIG. 6A and 6B, but with different restrictions onwhich radio resources can be used for transmitting which priorities ofdata. The exact manner in which scheduling allocation signalling anddata transmission signalling are configured in a given D2Dcommunications implementation is not significant to the principlesunderlying certain embodiment of the present disclosure. That is to say,the specific nature of the scheduling allocation signalling, and themanner in which the scheduling allocation signalling indicatescorresponding resources for data communication, may be in accordancewith any appropriate technique, such as those previously proposed fordevice-to-device communications.

For the example represented in FIG. 9 it is assumed the wirelesstelecommunications system for which the radio frame structure 900applies supports four different levels of data priority. These may bereferred to as priority level 1, priority level 2, priority level 3 andpriority level 4. Priority level 1 is for data having the highestpriority, priority level 2 is for data having the second highestpriority, priority level 3 is for data having the third highest priorityand priority level 4 is for data having the lowest priority.

A significant aspect of the subframe structure represented in FIG. 9 isthat certain subframes are reserved for certain priority communications.In this particular example every fourth subframe starting from SF1 isassumed to be reserved for priority level 1 data, as schematicallyindicated in FIG. 9 by the diagonal hatching in the subframes labelledSF1, SF5 and SF9. Every fourth subframe starting from SF2 is assumed tobe reserved for priority level 1 and 2 data, as schematically indicatedin FIG. 9 by the square hatching in the subframes labelled SF2, SF6 andSF10. Every fourth subframe starting from SF3 is assumed to be reservedfor priority level 1, 2 and 3 data, as schematically indicated in FIG. 9by the crossed-diagonal hatching in the subframes labelled SF3, SF7 andSF11. Finally, every fourth subframe starting from SF4 is assumed to beavailable for all protein levels, as schematically indicated in FIG. 9by the dot hatching in the subframes labelled SF4, SF8 and SF12.

A terminal device wishing to transmit data in a wirelesstelecommunications system implementing the radio frame structure of FIG.9 associates a priority status with the data to be transmitted (i.e.priority level 1, 2, 3 or 4). It will be appreciated the particularreasons why particular data are associated with particulate prioritiesare not significant to the principles underlying embodiments of thepresent disclosure and may depend on the specific implementation athand. The terminal device then selects resources to seek to use fortransmitting the data by taking account of the associated prioritylevel. For example, if the data are classified as priority level 1, theterminal device may seek to use resources in all subframes. However, ifthe data are classified as priority level 2, the terminal device mayseek to use resources in all subframes except for the subframes reservedfor priority level 1 (SF1, SF5, SF9). If the data are classified aspriority level 3, the terminal device may seek to use resources in onlyhalf the subframes, namely those available for all priority levels andthose reserved for priority levels 1, 2 and 3 (SF3, SF4, SF7, SF8, SF11,SF12). If the data are classified as priority level 4, the terminaldevice will avoid using resources in all subframes except for thoseavailable for all priority levels (SF4, SF8, SF12).

Thus, there are more radio resources available for transmitting higherpriority data than for transmitting lower priority data. This provides anatural mechanism for prioritising the likelihood of successfultransmission of data according to its associated priority level.Furthermore, a terminal device that has started transmitting highpriority data in a particular subframe reserved for data with thatpriority may preferentially obtain access to radio resources insubsequent subframes, even though these resources may be available toall priority levels, by virtue of having already begun transmitting.

A potential drawbacks with the approach represented in FIG. 9 is thatlow priority data may become “stuck” if the resources are continuallybeing used by higher priority data. To address this a terminal devicemay be configured to in effect upgrade the priority level for its dataif one or more criteria are met, for example if the data cannot be sentwithin a predefined period of time. For example, a terminal devicehaving low priority data for transmission may be configured to start atimer when the data is first queued for transmission, and if theterminal device fails to transmit the data, or to transmit the datacompletely, within a certain time frame, it may increase the prioritylevel of the data, for example by one level, to gain access to a widerrange of radio resources. The priority level could be retained as aterminal device internal variable, or as a variable set in response toreceiving signalling from another entity. The terminal device may theycontinue trying to transmit the data on resources associated with theupdated priority level. Again, if the data cannot be transmitted withina certain time (and/or other relevant criteria are met), the prioritylevel may be increased further still, and so on until the data issuccessfully transmitted. Various parameters may be used to control whena terminal device should update the priority status of data waiting fortransmission. For example, the decision to update the priority level maybe based on the time for which the data has remained pending, the sizeof the data to be transmitted, and potentially also the number of otherterminal devices contending for the available transmission resources.The relevant parameters may be specification defined, or may becontrolled from a coordinating entity, such as a base station.

The upgrade condition/criteria may be based on a single parameter or acombination of parameters, such as a single composite value determinedfrom a plurality of parameters. For example, the criteria may be basedon a value calculated from a combination of some or all of a buffersize, a waiting time and traffic priority. Each parameter may have aweighting factor. The weighting factors could, for example, be variableand configured by higher layers.

As well as providing schemes for interruption and prioritisation,similar principles may be used for managing the transfer ofdelay-tolerant data. For example, in one implementation a terminaldevice may wish to transmit a relatively large volume of delay-tolerantdata. In this respect, the fact the data is delay tolerant may beconsidered as classifying the data as low priority as compared to normalpriority data. The terminal device may issue a scheduling allocationmessage to indicate resources to be used in data communication regionsof a plurality of subsequent subframes for transmitting thedelay-tolerant data. The data may then be transmitted in the datacommunication regions of the subsequent subframes without requiringcorresponding scheduling allocation signalling in those subframes (i.e.a scheduling allocation message in one subframe may apply for aplurality of subframes). The terminal device may then proceed withtransmitting the data in selected resources corresponding to the datacommunication regions of the subsequent subframes while avoidingtransmissions in the scheduling allocation regions of the subsequentsubframes. In this respect the scheduling allocation regions of thesubsequent subframes may be considered as being reserved for use byhigher priority data (i.e. data which is not delay tolerant). If theterminal device recognises another terminal device issues a schedulingallocation message in one of the subframes, the terminal device may stoptransmitting the delay-tolerant data in subsequent data communicationregions, thereby releasing these radio resources for use by the highpriority (non-delay-tolerant) data.

While the above-described examples have focused on implementations inwhich the radio resources reserved for different priorities of data areseparated in the time domain, in accordance with other embodiments theradio resources may instead, or in addition, be reserved in thefrequency domain. For example, instead of reserving certain subframesfor various levels of priority, certain frequency resources in all, orsome, subframes, may be reserved for this purpose instead. In yet otherexamples, the radio resources reserved for urgent communications maycomprise scheduling allocation messages having particularcharacteristics, for example in terms of preambles, or time andfrequency of transmission.

The actual radio resources which are reserved for different levels ofpriority may be determined in various ways. For example, the specificresources to be reserved for the different levels of priority may bedefined in accordance with an operating standard for the wirelesstelecommunications system in which the terminal devices operate, or maybe communicated from a coordinating entity of the wirelesstelecommunications system, for example a base station. In other examplesthe radio resources reserved to allow terminal devices with highpriority data to transmit may not be predefined, but may depend onongoing traffic conditions. For example, there may simply be arequirement that any individual terminal device should not transmitcontinuously for longer than a threshold duration, and instead shouldavoid making transmissions in subframes according to a predefined cycle,for example after a given number of subframes of continuous transmissionthe terminal device should not make any transmissions for one (or more)subframes to allow other terminal devices with more urgent data toinitiate transmissions, for example by setting their own schedulingallocation signalling. The fraction of resources reserved for differentlevels of priority may be selected according to the expected levels oftraffic at the different priority levels.

Furthermore, while the example embodiments represented in FIGS. 6A, 6Band 9 have focused on embodiments in which the radio resourcessupporting the D2D communications are arranged in a continuous manner inboth time and frequency, it will be appreciated in other embodiments theradio resources supporting the D2D communications might not becontinuous in time and/or frequency. For example, rather than have acontinuous series of subframes supporting D2D communications, in anotherimplementation there may be gaps between the subframes. For example, theradio resources supporting the D2D communications link may, for example,comprise two 10 ms subframes in every 40 ms period. More generally, theradio resources supporting the D2D communication link may be scatteredin terms of time and frequency, for example to use particular resourceswithin a frame structure associated with a wireless telecommunicationssystem in which the D2D communications are being made. Thus, thespecific arrangement of radio resources comprising the D2Dcommunications link in any given implementations may be differentaccording to, for example, the manner in which the D2D communicationsare permitted to access radio resources used for other purposes, forexample for conventional communications between a base station andterminal devices in a communication cell of a wirelesstelecommunications system in which the D2D terminal devices areoperating. That is to say, the D2D radio frame structure might notmirror a conventional LTE radio frame structure. The D2D frame structuremight, however, have some basis in a conventional LTE frame structure.For example, the D2D frame structure might be based on radio resourcescomprising a defined subset of frequency resources and/or subframes of aconventional LTE frame structure.

As noted above, there are various ways in which the terminal devices candetermine a priority status for the data they are to transmit. Forexample, the priority status may be based on one or more of (i) alogical channel for the data, for example with data for certain logicalchannel is being classified as having a certain priority; (ii) a desiredquality of service for the data; (iii) an indication of priority for thedata received from a user of the first terminal device; (iv) anapplication within the first terminal device with which the data isassociated; (v) the nature of any connection between the first terminaldevice and a core network of a wireless telecommunications system inwhich the first terminal device is operating (e.g. whether in idle orconnected mode); (vi) a classification type for the terminal device (forexample, a terminal device associated with law enforcement or rescueservices may be considered to always generate high priority data), (vii)a classification type for an application associated with the data; and(viii) a classification type for a service associated with the data.

Although the above-described examples have focused on implementations inthe context of an LTE-based wireless telecommunications system, it willbe appreciated similar principles can be adopted for in wirelesstelecommunications systems operating in accordance with other protocols.In some example implementations the wireless telecommunications systemmight comprise terminal devices which are configured to communicate withone another in a device-to-device manner without there being anyinfrastructure equipment (e.g. a base station) to also provide forcommunications through the infrastructure equipment. In some respectssuch an approach corresponds with an implementation in which theterminal devices may in fact be considered to be always out of coverage.

Thus a method of operating a first terminal device to transmit data to asecond terminal device by performing device-to-device communication isdisclosed. The method comprises selecting radio resources, e.g.particular subframes (or other defined time blocks) or frequencies, onwhich to transmit the data to the second terminal device based on apriority status associated with the data, whereby certain radio resourceare reserved for use in association with data classified as highpriority. There is also disclosed a method of operating the secondterminal device to receive data from the first terminal device. Themethod comprises receiving data from the first terminal device using theselected radio resources; determining if another terminal device istransmitting data on a radio resource which is not selected fortransmitting data by the first terminal device and which is reserved fortransmitting data classified as having a high priority; and, if so,stopping reception of data from the first terminal device on theselected radio resources and instead seeking to receive furthertransmissions from the other terminal device. The disclosed methods thusprovide a mechanism whereby a terminal device with high priority data totransmit is provided with an opportunity to interrupt on-goingcommunications between the first and second terminal devices.

Further particular and preferred aspects of the present invention areset out in the accompanying independent and dependent claims. It will beappreciated that features of the dependent claims may be combined withfeatures of the independent claims in combinations other than thoseexplicitly set out in the claims.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, define, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

Respective features of the present disclosure are defined by thefollowing numbered paragraphs:

Paragraph 1. A method of operating a first terminal device to transmitdata to a second terminal device by performing device-to-devicecommunication, wherein the method comprises:

-   -   selecting radio resources on which to transmit the data to the        second terminal device based on a priority status associated        with the data; and transmitting the data to the second terminal        device using the selected radio resources.

Paragraph 2. The method of paragraph 1, wherein the device-to-devicecommunication is performed over a radio interface comprising radioresources divided into a plurality of time blocks and selecting radioresources on which to transmit the data to the second terminal devicecomprises selecting one or more time blocks in which to transmit thedata to the second terminal device, and/or, wherein the device-to-devicecommunication is performed over a radio interface comprising radioresources divided into a plurality of frequencies and selecting radioresources on which to transmit the data to the second terminal devicecomprises selecting one or more frequencies on which to transmit thedata to the second terminal device

Paragraph 3. The method of paragraph 1 or 2, wherein the radio resourceson which to transmit the data are selected from a set of radio resourceswhich excludes a predefined subset of radio resources if the data isassociated with a first priority status and are selected from a set ofradio resources which does not exclude the predefined subset of radioresources if the data is associated with a second priority status,wherein the first priority status indicates the data has a lowerpriority than data associated with the second priority status.

Paragraph 4. The method of paragraph 3, wherein the predefined set ofradio resources comprises a temporally repeating pattern of radioresources in which transmissions of the data associated with the firstpriority status are to be avoided.

Paragraph 5. The method of paragraph 3 or 4, wherein the predefined setof radio resources is established in dependence on an operating standardfor the first terminal device and/or in dependence on signallingreceived from a network entity of a wireless telecommunications systemin which the first terminal device is operating.

Paragraph 6. The method of paragraph 3, 4 or 5, wherein the radioresources on which to transmit the data are selected from a set of radioresources which excludes both the predefined subset of radio resourcesand a further predefined subset of radio resources if the data isassociated with a further priority status and are selected from a set ofradio resources which does not exclude the further predefined set ofradio resources if the data is associated with the first priority statusor the second priority status, wherein the further priority statusindicates the data has a lower priority than data associated with thefirst priority status and the second priority status.

Paragraph 7. The method of any of paragraphs 1 to 6, further comprisingthe first terminal device determining if another terminal device istransmitting data using a radio resource which is not selected by thefirst terminal device for transmitting the data device based on itspriority status.

Paragraph 8. The method of paragraph 7, further comprising the firstterminal device cancelling transmissions of the data on one or more ofthe selected radio resources following a determination that anotherterminal device is transmitting data on a radio resource which is notselected by the first terminal device for transmitting the data devicebased on its priority status.

Paragraph 9. The method of paragraph 8, further comprising the firstterminal device seeking to receive further transmissions from theterminal device transmitting data in a radio resource which is notselected for transmitting data by the first terminal device on radioresources in which the first terminal device has cancelled its owntransmissions.

Paragraph 10. The method of any of paragraphs 1 to 9, wherein thepriority status associated with data is determined based on one or moreof:

-   -   (i) a logical channel for the data;    -   (ii) a quality of service requirement for the data;    -   (iii) an indication of priority for the data received from a        user of the first terminal device;    -   (iv) an application within the first terminal device with which        the data is associated;    -   (v) the nature of any connection between the first terminal        device and a core network of a wireless telecommunications        system in which the first terminal device is operating;    -   (vi) a classification type for the terminal device;    -   (vii) a classification type for an application associated with        the data;    -   (viii) a classification type for a service associated with the        data.

Paragraph 11. The method of any of paragraphs 1 to 10, furthercomprising the first terminal device associating the data with anupdated priority status and selecting one or more radio resources onwhich to transmit the data to the second terminal device based on theupdated priority status if it is determined it would take longer than apredefined threshold duration to transmit the data to the secondterminal device on radio resources selected based on the data's prioritystatus prior to being updated.

Paragraph 12. The method of any of paragraphs 1 to 11, wherein atransmission characteristic for data transmitted by the first terminaldevice is selected in dependence on the priority status for the data.

Paragraph 13. The method of paragraph 12, wherein the transmissioncharacteristic comprises a transmission power.

Paragraph 14. The method of any of paragraphs 1 to 13, wherein themethod is performed in a wireless telecommunications system comprisingthe first and second terminal devices and a base station, and whereinthe method further comprises the first terminal device exchangingfurther data with the base station.

Paragraph 15 The method of any of paragraphs 1 to 14, wherein the datato be transmitted by the first terminal device comprises user-plane dataand/or control data indicating radio resources the first terminal deviceintends to use to transmit other data.

Paragraph 16. A terminal device configured to transmit data to a secondterminal device by performing device-to-device communication, whereinthe terminal device comprises a controller unit and a transceiver unitconfigured to operate together to select radio resources on which totransmit the data to the second terminal device based on a prioritystatus associated with the data; and to transmit the data to the secondterminal device using the selected radio resources.

Paragraph 17. Circuitry for a terminal device configured to transmitdata to a second terminal device by performing device-to-devicecommunication, wherein the circuitry comprises a controller element anda transceiver element configured to operate together to cause theterminal device to select radio resources on which to transmit the datato the second terminal device based on a priority status associated withthe data; and to transmit the data to the second terminal device usingthe selected radio resources.

Paragraph 18. A method of operating a second terminal device to receivedata from a first terminal device by performing device-to-devicecommunication, wherein the method comprises:

-   -   receiving data from the first terminal device using radio        resources selected by the first terminal device for transmitting        the data;    -   determining if another terminal device is transmitting data on a        radio resource which is not selected for transmitting data by        the first terminal device and which is reserved for transmitting        data classified as having a high priority; and, if so,    -   stopping reception of data from the first terminal device on the        selected radio resources and instead seeking to receive further        transmissions from the other terminal device.

Paragraph 19. A terminal device configured to receive data from atransmitting terminal device by performing device-to-devicecommunication, wherein the terminal device comprises a controller unitand a transceiver unit configured to operate together to: receive datafrom the transmitting terminal device using radio resources selected bythe first terminal device for transmitting the data; determine ifanother terminal device is transmitting data on a radio resource whichis not selected for transmitting data by the transmitting terminaldevice and which is reserved for transmitting data classified as havinga high priority; and, if so, to stop reception of data from thetransmitting terminal device on the selected radio resources and insteadseek to receive further transmissions from the other terminal device.

Paragraph 20. Circuitry for a terminal device configured to receive datafrom a transmitting terminal device by performing device-to-devicecommunication, wherein the circuitry comprises a controller element anda transceiver element configured to operate together to cause theterminal device to: receive data from the transmitting terminal deviceusing radio resources selected by the first terminal device fortransmitting the data; determine if another terminal device istransmitting data on a radio resource which is not selected fortransmitting data by the transmitting terminal device and which isreserved for transmitting data classified as having a high priority;and, if so, to stop reception of data from the transmitting terminaldevice on the selected radio resources and instead seek to receivefurther transmissions from the other terminal device.

REFERENCES

[1] US 2013/0012221

[2] US 2012/0265818

[3] LTE for UMTS: OFDMA and SC-FDMA Based Radio Access, Harris Holma andAntti Toskala, Wiley 2009, ISBN 978-0-470-99401-6.

[4] R2-133840, “CSMA/CA based resource selection,” Samsung, published at3GPP TSG-RAN WG2 #84, San Francisco, USA, 11-15 Nov. 2013.

[5] R2-133990, “Network control for Public Safety D2D Communications”,Orange, Huawei, HiSilicon, Telecom Italia, published at 3GPP TSG-RAN WG2#84, San Francisco, USA, 11-15 Nov. 2013.

[6] R2-134246, “The Synchronizing Central Node for Out of Coverage D2DCommunication”, General Dynamics Broadband UK, published at 3GPP TSG-RANWG2 #84, San Francisco, USA, 11-15 Nov. 2013.

[7] R2-134426, “Medium Access for D2D communication”, LG ElectronicsInc, published at 3GPP TSG-RAN WG2 #84, San Francisco, USA, 11-15 Nov.2013.

[8] R2-134238, “ D2D Scheduling Procedure”, Ericsson, published at 3GPPTSG-RAN WG2 #84, San Francisco, USA, 11-15 Nov. 2013.

[9] R2-134248, “Possible mechanisms for resource selection inconnectionless D2D voice communication”, General Dynamics Broadband UK,published at 3GPP TSG-RAN WG2 #84, San Francisco, USA, 11-15 Nov. 2013.

[10] R2-134431, “Simulation results for D2D voice services usingconnectionless approach”, General Dynamics Broadband UK, published at3GPP TSG-RAN WG2 #84, San Francisco, USA, 11-15 Nov. 2013.

[11] “D2D Resource Allocation under the Control of BS”, Xiaogang R. etal, University of Electronic Science and Technology of China,https://mentor.ieee.org/802.16/dcn/13/16-13-0123-02-000n-d2d-resource-allocation-under-the-control-of-bs.docx

[12] US20130170387

[13] US20120300662

1. A method of operating a first terminal device to transmit data to asecond terminal device by performing device-to-device communication,wherein the method comprises: selecting radio resources on which totransmit the data to the second terminal device based on a prioritystatus associated with the data; and transmitting the data to the secondterminal device using the selected radio resources.
 2. The method ofclaim 1, wherein the device-to-device communication is performed over aradio interface comprising radio resources divided into a plurality oftime blocks and selecting radio resources on which to transmit the datato the second terminal device comprises selecting one or more timeblocks in which to transmit the data to the second terminal device,and/or, wherein the device-to-device communication is performed over aradio interface comprising radio resources divided into a plurality offrequencies and selecting radio resources on which to transmit the datato the second terminal device comprises selecting one or morefrequencies on which to transmit the data to the second terminal device.3. The method of claim 1, wherein the radio resources on which totransmit the data are selected from a set of radio resources whichexcludes a predefined subset of radio resources if the data isassociated with a first priority status and are selected from a set ofradio resources which does not exclude the predefined subset of radioresources if the data is associated with a second priority status,wherein the first priority status indicates the data has a lowerpriority than data associated with the second priority status.
 4. Themethod of claim 3, wherein the predefined set of radio resourcescomprises a temporally repeating pattern of radio resources in whichtransmissions of the data associated with the first priority status areto be avoided.
 5. The method of claim 3, wherein the predefined set ofradio resources is established in dependence on an operating standardfor the first terminal device and/or in dependence on signallingreceived from a network entity of a wireless telecommunications systemin which the first terminal device is operating.
 6. The method of claim3, wherein the radio resources on which to transmit the data areselected from a set of radio resources which excludes both thepredefined subset of radio resources and a further predefined subset ofradio resources if the data is associated with a further priority statusand are selected from a set of radio resources which does not excludethe further predefined set of radio resources if the data is associatedwith the first priority status or the second priority status, whereinthe further priority status indicates the data has a lower priority thandata associated with the first priority status and the second prioritystatus.
 7. The method of claim 1, further comprising the first terminaldevice determining if another terminal device is transmitting data usinga radio resource which is not selected by the first terminal device fortransmitting the data based on its priority status.
 8. The method ofclaim 7, further comprising the first terminal device cancellingtransmissions of the data on one or more of the selected radio resourcesfollowing a determination that another terminal device is transmittingdata on a radio resource which is not selected by the first terminaldevice for transmitting the data based on its priority status.
 9. Themethod of claim 8, further comprising the first terminal device seekingto receive further transmissions from the terminal device transmittingdata in a radio resource which is not selected for transmitting data bythe first terminal device on radio resources in which the first terminaldevice has cancelled its own transmissions.
 10. The method of claim 1,wherein the priority status associated with data is determined based onone or more of: (i) a logical channel for the data; (ii) a quality ofservice requirement for the data; (iii) an indication of priority forthe data received from a user of the first terminal device; (iv) anapplication within the first terminal device with which the data isassociated; (v) the nature of any connection between the first terminaldevice and a core network of a wireless telecommunications system inwhich the first terminal device is operating; (vi) a classification typefor the terminal device; (vii) a classification type for an applicationassociated with the data; (viii) a classification type for a serviceassociated with the data.
 11. The method of claim 1, further comprisingthe first terminal device associating the data with an updated prioritystatus and selecting one or more radio resources on which to transmitthe data to the second terminal device based on the updated prioritystatus if it is determined it would take longer than a predefinedthreshold duration to transmit the data to the second terminal device onradio resources selected based on the data's priority status prior tobeing updated.
 12. The method of claim 1, wherein a transmissioncharacteristic for data transmitted by the first terminal device isselected in dependence on the priority status for the data.
 13. Themethod of claim 12, wherein the transmission characteristic comprises atransmission power.
 14. The method of claim 1, wherein the method isperformed in a wireless telecommunications system comprising the firstand second terminal devices and a base station, and wherein the methodfurther comprises the first terminal device exchanging further data withthe base station.
 15. The method of claim 1, wherein the data to betransmitted by the first terminal device comprises user-plane dataand/or control data indicating radio resources the first terminal deviceintends to use to transmit other data.
 16. A terminal device configuredto transmit data to a second terminal device by performingdevice-to-device communication, wherein the terminal device comprises acontroller unit and a transceiver unit configured to operate together toselect radio resources on which to transmit the data to the secondterminal device based on a priority status associated with the data; andto transmit the data to the second terminal device using the selectedradio resources.
 17. Circuitry for a terminal device configured totransmit data to a second terminal device by performing device-to-devicecommunication, wherein the circuitry comprises a controller element anda transceiver element configured to operate together to cause theterminal device to select radio resources on which to transmit the datato the second terminal device based on a priority status associated withthe data; and to transmit the data to the second terminal device usingthe selected radio resources.
 18. (canceled)
 19. A terminal deviceconfigured to receive data from a transmitting terminal device byperforming device-to-device communication, wherein the terminal devicecomprises a controller unit and a transceiver unit configured to operatetogether to: receive data from the transmitting terminal device usingradio resources selected by the first terminal device for transmittingthe data; determine if another terminal device is transmitting data on aradio resource which is not selected for transmitting data by thetransmitting terminal device and which is reserved for transmitting dataclassified as having a high priority; and, if so, to stop reception ofdata from the transmitting terminal device on the selected radioresources and instead seek to receive further transmissions from theother terminal device.
 20. (canceled)